Earthquakes are rocking Iceland's Bardarbunga volcano, adding to concerns that magma movements may trigger an eruption that could hinder air traffic.
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Iceland's Met Office says two earthquakes measuring over magnitude 5 shook the volcano under the vast Vatnajokull glacier on Wednesday. Some 500 quakes have hit the area since midnight.
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Iceland's aviation alert level remains at orange, the second highest.
On Sunday, the Met Office lowered the alert level, saying there was no sign of an imminent eruption at Bardarbunga.
In 2010, Iceland's Eyjafjallajokul volcano erupted and sparked off a week of international aviation chaos. Some 100,000 flights were cancelled after aviation officials closed Europe's air space for five days out of fear that volcanic ash could harm jet engines.